Re: [patch 3/6] mmu_notifier: invalidate_page callbacks

Andrew Morton
2008-02-16T03:39:50Z

On Thu, 14 Feb 2008 22:49:02 -0800 Christoph Lameter <clameter@sgi.com> wrote:

> Two callbacks to remove individual pages as done in rmap code
>
> invalidate_page()
>
> Called from the inner loop of rmap walks to invalidate pages.
>
> age_page()
>
> Called for the determination of the page referenced status.
>
> If we do not care about page referenced status then an age_page callback
> may be be omitted. PageLock and pte lock are held when either of the
> functions is called.

The age_page mystery shallows.

It would be useful to have some rationale somewhere in the patchset for the
existence of this callback.

> #include <asm/tlbflush.h>
>
> @@ -287,7 +288,8 @@ static int page_referenced_one(struct pa
> if (vma->vm_flags & VM_LOCKED) {
> referenced++;
> *mapcount = 1; /* break early from loop */
> - } else if (ptep_clear_flush_young(vma, address, pte))
> + } else if (ptep_clear_flush_young(vma, address, pte) |
> + mmu_notifier_age_page(mm, address))
> referenced++;

The "|" is obviously deliberate. But no explanation is provided telling us
why we still call the callback if ptep_clear_flush_young() said the page
was recently referenced. People who read your code will want to understand
this.

> /* Pretend the page is referenced if the task has the
> @@ -455,6 +457,7 @@ static int page_mkclean_one(struct page
>
> flush_cache_page(vma, address, pte_pfn(*pte));
> entry = ptep_clear_flush(vma, address, pte);
> + mmu_notifier(invalidate_page, mm, address);

I just don't see how ths can be done if the callee has another thread in
the middle of establishing IO against this region of memory.
->invalidate_page() _has_ to be able to block. Confused.